The behavior of mammalian muscles, muscle receptors, alpha and gamma motoneurons and motor units has been studied for the last twenty five years. We propose to continue our quantitative studies of the interactions between these elements of the feline peripheral neuromuscular system using new experimental techniques of random stimulation and new data processing and analysis techniques known as "Wiener Kernel" analysis. Unlike previous studies, we are emphasizing the use of simultaneous stimulation of several elements to study their effect on some other component. For example, we shall test the effect of: 1) concurrently changing the length of two muscles on the membrane potential of a homonymous, synergist or antagonist motoneuron; 2) concurrently activating several motor units on type Ia, II and Ib afferent spike trains arising from the same muscle; 3) concurrently stimulating several gamma efferents on Ia and II afferent spike trains. Our proposal also calls for the development of new computational procedures which can quantify the linear and nonlinear effects of each input on the output, as well as any interactive effects between inputs. To interpret the quantitative results of these experiments, we shall continue to develop powerful computer simulation models of the systems being studied, subjecting them to the same tests being applied to the experimental animals. Our results should enable neurophysiologists to appreciate the deeper significance of signals now being monitored at the same level in human subjects in other laboratories. To execute this program requires coordination of the activities of three highly specialized laboratories, each capable of state-of-the art experimentation.